1. Field of the Invention
This invention relates to a thermostatic expansion valve for use in refrigerating systems of car air conditioners.
2. Description of Related Art
As shown in Japanese Laid-open Patent No. 6-185833, a conventional thermostatic expansion valve generally comprises a valve shell that has a high-pressure refrigerant passage through which liquid refrigerant to be reduced in pressure travels and a low-pressure refrigerant passage through which vapor-phase refrigerant travels. A valve hole is formed midway of the high-pressure refrigerant passage. A valve member is disposed to move to and away from the valve hole to change the opening rate of the valve hole. A pressure-operating housing includes a diaphragm for driving the valve member through a driving rod to control movements of the valve member. An air-tight chamber is partitioned by the diaphragm and filled with heat-sensitive gas, and mounted on the valve shell to detect the temperature of gaseous-phase refrigerant. A plug member shuts an outer wall opening provided in an outer wall of the pressure-operating housing after heat-sensitive gas is fully introduced into the air-tight chamber through the outer wall opening.
In the conventional thermostatic expansion valve above, the plug member, which has a flange portion, is typically fixed to the housing outer wall in such a manner that a portion of the spherical surf ace of the plug member is in direct contact with the opening edge of the housing outer wall and is secured thereto by projection welding. The flange portion of the plug member 16 is fixed to the housing outer wall by a solder-welding portion to seal the opening. In this method, the projection welding is used only for provisional fixture of the plug member, and the seal of the opening is established by the soldering.